Valves of this type are particularly used within the food, beverage, and medical industries where demands on hygiene are great. The presence of a diaphragm which separates the medium from the manoeuvring part of the valve makes this valve particularly suited for use in a sterile environment.
Also in recent years problems have arisen in connection with genetic engineering techniques, where authorities issue very strict rules about containment inside the fermentation tanks of genetically engineered microorganisms or cell lines for extended periods of time, such as 3 to 4 months for the fermentation of a cell line.
Hitherto known diaphragm valves have, however, turned out to give rise to problems, both in terms of failing sterile technical properties and in use in connection with sampling from the medium.
The diaphragm valve known from French patent No. 927,290 is an example of such a valve where the diaphragm rests on a valve seat being designed in a rib extending across the flow channel. This rib is provided with several pockets and corners in which the medium may be deposited so that the valve firstly is difficult to clean and sterilize, and secondly, will cause an uneven sampling, both since the uneven flow conditions cause an uneven mixing of the medium, and due to the risk of stagnant media. Also, the bad flow conditions cause a great loss of pressure.
French patent No. 1,200,849 (Nuyens) is another example of such a valve. However, the valve of that patent cannot be mounted so that the diaphragm in closed position forms a closure against the container wall and partly becomes an integral part thereof, but a stagnant container volume (dead volume or leg) will be formed in the valve inlet.
The valve cannot be used for sampling from suspended fluids, since the stagnant volume of fluid in the valve inlet will have a higher concentration of suspended material than in the container where the suspension is kept in mixture by stirring means.
Another example of a diaphragm valve of a related type is disclosed in U.S. Pat. No. 4,653,526 (Hoiss) relating to a diaphragm valve for removing samples from a pipeline. In connection with that patent corresponding problems relating to dead volumes in the valve inlet arise.
An example of a type of valve used as a sterilizable drain valve can be seen in U.S. Pat. No. 4,836,236 (Ladisch). The valve according to that patent also exhibits a valve chamber giving problems in connection with sterilisation and complete drainage of said chamber. Also, that type of valve is in no way suitable for vertical mounting for taking samples from the content of a tank.
A further disadvantage with many of the prior art diaphragm valves is that the diaphragm material during operation must be deformed considerably increasing the risk of cracks in or bursting of the diaphragm.
The reality of this problem is seen in that the valve in U.S. Pat. No. 4,836,236 is provided with special sealing means which safeguard against leakage by diaphragm rupture.